(1) Field of the Invention
The present invention relates to an emergency call control apparatus for a mobile communication system, and more particularly to an emergency call control apparatus which is capable of smoothly effecting handoff control even when a mobile station moves from a service zone into another service zone while engaging in an emergency call in a mobile communication system.
More specifically, the present invention is concerned with an emergency call control apparatus for a CDMA (Code Division Multiple Access) mobile communication system.
Handoff control refers to a capability to maintain communication with a mobile station in a call without interruptions when the mobile station moves from a service zone to another service zone while engaging in the call, and is also called "handover".
(2) Description of the Related Art
Generally, the number of radio channels available between mobile stations and a base station in a mobile communication system is very small. The limited number of available radio channels may possibly result in a situation where an emergency call from a mobile station cannot be connected when there is a request to connect such an emergency call to a police station or a fire department from the mobile station to the base station while the radio channels are being congested. Heretofore, various efforts have been made to connect an emergency call with priority in order to avoid such a situation.
The conventional attempts are based on the assumption that a mobile station which has made a request to connect an emergency call in a service zone does not move from that service zone while the mobile station is engaging in the emergency call. No consideration has been given to possible movement of the mobile station to another service zone during the emergency call. Therefore, although an emergency call from a mobile station in a first service zone can be connected with priority regardless of the radio channels being congested in the first service zone, when the mobile station moves to a second service zone adjacent to the first service zone, the emergency call can possibly be disconnected if the radio channels are congested in the second service zone. Stated otherwise, in a handoff, a radio channel is not assigned with priority to the emergency call in the second service zone to which the mobile station has moved.